It will destroy only Alderaan. The main conflict is not between the rebel alliance and the empire, it is between Luke and Vader and that's where I want to keep the focus. The only way I could see it working in this narrative is through some sort of montage of it destroying different planets, but that doesn't really fit in with the style of the rest of the story, I'm not crazy about the idea of creating several custom shots of different planets blowing up, and it would feel disjointed and distract from the main narrative ultimately to not do very much, if anything, for the story.